Radio receiving apparatus



March 31, 1942. M. J. PIFER RADIO RECEIVING APPARATUS Filed March 7, 1940 B POWE R SUPPLY *INVENTIOR Mae/om [PM-2 ORNEY ATT Patented Mar. 31, 1942 UNITED STATES PATENT OFFICE RADIO RECEIVING APPARATUS Marion J. Pifer, Williamsvillc, N. Y., assignor to Colonial Radio Corporation, Buffalo, N. Y., a corporation of New York Application March 7, 1940, Serial No. 322,709

7 Claims.

This application relates to radioreceiving apparatus intended to operate under conditions where it is subject to so-called man-made static. While my invention may be generally useful under all conditions where such interference is encountered, it is particularly useful in radio receiving apparatus employed in automobiles, boats, airplanes and the like, where motors and particularly internal combustion motors are operating and where there are likely to be high frequency disturbances set up by the ignition apparatus.

-In such radio receiving apparatus, it is customary to mount the receiving apparatus per se (which usually comprises the chassis With the tubes and interstage coupling transformers and the like) within a conducting grounded metallic case for the purpose of protecting the apparatus mechanically and also of shielding it from extraneous electrical disturbances. Ordinarily, however, the current source for energizing the apparatus is not enclosed within the shielding case, and the leads which carry the power from the external source into the case pick up and carry into the case disturbances which, if not eliminated, are likely to produce annoying noises in the received signal or even to obliterate it entirely.

I have found that in accordance with my invention I am able to prevent such disturbances picked up upon the external cable from causing any harmful effects in the-operation of the receiver and I am able to do this in accordance with the principles of my invention with a relatively simple form of apparatus which is extremely inexpensive to build and install, and once installed, is unlikely to get out of order or give trouble.

It is an object of my invention to provide a radio receiving system which is relatively free from the effect of man-made static carried into the receiver over the power supply wiring, and which can be produced at relatively little expense.

It is a further object of my invention to provide a new, highly efficient and economical form of filter for separating the currents representing undesired disturbances from the necessary currents required to operate the receiver.

It is a further object of my invention to provide an inductanceless condenser which is extremely effective for filtering purposes, in a relatively simple compact and inexpensive form, and which is for all practical purposes, self-shielding.

Still other objects of my invention will be apparent from the specification.

In this application I have particularly pointed out and distinctly claimed the part, improvement or combination which I claim as my invention or discovery, and I have explained the principles thereof and the best mode in which I have contemplated applying those principles, so as to distinguish my invention from other inventions.

In the drawing:

Figure 1 is a cross-sectional diagrammatic view of a radio receiver embodying my invention;

Fig. 2 is a plan View of the inductanceless condenser plate before mounting in the receiver case; and

Fig. 3 is a side View of the same applied to the receiver housing to form an inductanceless condenser.

Referring now more particularly to Fig. 1, i represents diagrammatically the casing containing the radio receiver, the latter being shown in merely diagrammatic form. The casing usually comprises a metallic box I, having a metallic cover 2, within which is positioned the various parts of the receiver diagrammatically illustrated by tubes 3 and B power supply 1. Many forms of radio receivers being Well-known in the art,

the circuits thereof are not illustrated in detail.

It will be understood that the casing l is usually grounded, and when the cover is inposition, constitutes a shield preventing the apparatus positioned within the casing from picking up extraneous electrical disturbances which would otherwise be picked up and interfere with the desired signal. In the usual form of such receivers, the source of power is ordinarily not withinthe shielding case, and in the present instance, power to operate the receiver may be supplied from source 9 which may be the storage battery of an automobile, boat or the like, or a motor-generator, dynamotor, or the like, one side of which is ordinarily grounded and the other side of which is connected to the power circuits within the receiver.

For a number of reasons not necessary tobe discussed here, the wiring from the source 9 may carry into the interior of the casing I, currents or voltages representing these undesired and disturbing effects. These may be transferred into the sensitive receiving circuits by conduction, or within the casing itself there maybe produced magnetic or electro-static fields which impress-these disturbing efiects upon the sensitive circuits of the tubes 3 and particularly the grid circuits 4 thereof. To prevent this, I force the rent from condenser 8 may then be passed to the tube circuits of the tubes as indicated by heating j line 5 and also to the B power supply 1 which may be the usual vibrator, transformer, and rectifier, thence through to the various screen and plate circuits of the tubes. The switch 6 repre-' sents the usual on-ofi switch of the receiver and may be operated by a suitable control projecting.

through the casing I or by remote control 'if desired. It is desirable to provide a choke 30 between terminal and switch 6, and this may be satisfactorily provided by coiling up a few turns, perhaps half a dozen, of the lead wire extending from 2!) to 6, thereby providing a small inductance between terminal 20 and the load circuit.

It has been suggested that a condenser should be mounted within the case I and connecting the supply line to ground for the purpose of draining off or bypassing the undesired electrical disturbances. I have found however that when an ordinary condenser is so used, it does not operate as satisfactorily as desired. No matter how short the leads to the condenser are made, even down to as little as A; of an inch, the inductance thereof is entirely too high to make a first class filter for such disturbances, which may have components of very high frequency. I have discovered that by using the receiver case as the grounded electrode or plate of the condenser and by using a fiat conducting plate placed against the casing, but insulated from it as the other electrode, I am able to obtain an inductanceless condenser provided I can make the leads from the circuit to be filtered to this condenser of zero effective length. I am able to accomplish this effective zero length of lead by bringing the circuit to be filtered to the condenser plate outside the housing and making the current flow through the entire length of the plate before it is distributed to the load circuit. I also provide a grounded shielding plate within the casing which covers the entering lead and the ungrounded condenser electrode in such a manner as to prevent any exposure of the lead or the plate itself to the sensitive wiring within the housing.

Referring now more particularly to Figs. 2 and 3, I is the wall of the housing, to which I secure the condenser plate and its shielding plate together with its insulation, the latter being formed as a single unitary article so that in assembly all that is necessary is to place the condenser assembly in position and secure it in place as by means of rivets II. While I have shown the condenser in this instance as mounted within the casing, this is not essential, and the condenser may be mounted on the outside of the easing if desired.

The condenser assembly itself comprises the shielding plate II], which may be made rectangular in shape and a little larger than the condenser plate which it is to shield. At one end it may be provided with a cylindrical extension I2, extending normally therefrom and preferably, but not necessarily, formed by stamping and bending. In the form shown, the metal of the plate is bent around into cylindrical form to abut together as at I3 and slightly cut away as at I4 to facilitate the bending and forming, and to provide room for insertion of the condenser electrode and insulation within the extension I2.

The fingers or lugs I5 may be struck downwardly and outwardly from the cylindrical extension I2 if desired, and an insulating bushing I60. may be inserted therein, which bushing may have a conducting eyelet or rivet IBb within it. Theungrounded side of the condenser may be formed by a plate II which may be rectangular in shape and at its upper end may have a finger I8 extending beyond the rectangular portion and bent upwardly to pass through the bushing andeyelet and to terminate at I9 forming a terminal towhich the conductor from source 9 may be connected.

The opposite end of plate Il may have a finger formed thereon projecting in the opposite direction through an opening in the shielding plate In and may terminate in terminal portion 20 to which the lead within the case to the heating circuit of the tubes may be connected. An insulating bushing 2| may be interposed between the finger 20 and the plate III. After passing through the opening to plate In the finger 20 may be bent down upon the bushing and then again bent upwardly, thereby serving to anchor the lower end of the condenser plate in position against the shielding plate and to form a lug to which wiring may be readily soldered.

The top end of the condenser plate may be held in position by the upper end offinger I8 which extends through the bushing within the tubular extension I2 from the shielding plate III. For insulating the condenser plate from the shielding plate and from the receiver casing itself, a layer of dielectric material is preferably provided on both sides of the condenser plate. This may be in the form of ordinary so-called fish paper, a little more than twice the length of the condenser plate and slightly wider than the same, folded in the middle and positioned both below and above the condenser plateas clearly shown by I6. The fish paper may have fingers 22 and 23 at its upper end projecting into the tubular extension I2 for the purpose of holding the fish paper in position before assembly onto the receiver case.

I have found that very satisfactory results are obtained in the ordinary automobile radio receiver as now manufactured when the condenser plate itself is of the order of of an' inch by 1% of an inch and when the shielding plate is made slightly larger. The shielding plate .and the condenser plate I! may be made of ordinary steel stamping stock. This construction has a capacity of the order of 250 m. m. f. and with it, I am able to obtain very satisfactory filtering in present-day automobile receivers.

It will be seen that I have produced a" very simple, economical, reliable andsatisfactory system for eliminating undesired disturbances such as motor noise and the like, and it will be understood that while I have shown and described certain preferred embodiments of my invention, modifications and changes may be madeatherein without departing from the spirit' and scope of my invention, as will be" clear to those skilled intheart.

having a plurality of tubes having circuits to be supplied with current from a source external to said case, of a condenser positioned within said case, one electrode of which is formed by a portion of said case, said condenser comprising a conducting plate insulated from said case, and secured against the inside thereof, and having at one end a finger on said plate passing through an opening in said case for connection to said source, a conducting shield covering said plate and having a tubular extension at one end thereof surrounding said finger, and a connection within the case from the other end of said plate to the circuits of said tubes, said shield covering said plate and said finger within said case and preventing exposure thereof to leads within said case of the path of currents from said source.

2. The combination with a radio receiver having a grounded metallic case, said radio receiver having a plurality of tubes having circuits to be supplied with current from a source external to said case, of a condenser positioned within said case, said condenser comprising a conducting plate insulated from said case, and secured against the inside thereof, and having at one end a finger on said plate passing through an opening on said case for connection to a source, a conducting shield covering said plate, said shield having at one end thereof an integral tubular extension at right angles to the plane thereof, said extension surrounding said finger, and a connection within the case from the other end of said plate to the circuits of said tubes, said shield covering said plate and said finger within said case and preventing exposure to leads Within said case of the path of currents from said source up to said connection.

3. A new article of manufacture consisting of a condenser plate and shield therefor, constructed and arranged to be secured to a conducting plate and to form therewith an inductanceless condenser, formed of a shielding plate having a tubular extension at one end thereof, a conducting plate positioned upon said shielding plate and insulated therefrom and having a finger extending through said tubular extension and having another finger at the opposite end thereof extending through an opening in said shielding plate.

4. A new article of manufacture consisting of a condenser plate and shield therefor constructed and arranged to be secured to a conducting plate and to form therewith an inductanceless condenser, formed of a shielding plate having at one end thereof a tubular extension projecting normally therefrom, to one side thereof, a conducting plate mounted on said shielding plate on the side to which said extension projects and insulated from said shielding plate, and having a finger projecting through said tubular extension, and having at its opposite end a second finger projecting in the opposite direction through an opening in said shielding plate and securing said conducting plate in position on said shielding plate.

5. A new article of manufacture consisting of a condenser plate and shield therefor constructed and arranged to be secured to a conducting plate and to form therewith an inductanceless condenser, formed of a shielding plate having at one end thereof a tubular extension projecting normally therefrom, a conducting plate mounted on said shielding plate and having a finger extending through said extension and insulatingly secured therein to fasten one end of said conducting plate to said shielding plate, and having a finger extending from the opposite end thereof and passing through said shielding plate and insulatingly secured in position to fasten the other end of said conducting plate to said shielding plate, and a layer of dielectric material interposed between said plates.

6. In combination with a radio receiver having a grounded metallic container, said radio receiver having a plurality of tubes having circuits to be supplied with current from a source external to said container, a condenser element comprising a conducting plate secured against one wall of said container but insulated therefrom, said plate and a portion of said container forming respectively the two electrodes of a substantially inductanceless condenser, said plate having at opposite ends a pair of terminals extending in opposite directions, one of said terminals passing through said container and being insulated therefrom whereby one terminal projects outwardly from said case and one projects inwardly in said case, a connection from said outwardly projecting terminal to said source, a connection from the inwardly projecting terminal to the circuits of said tubes, and a grounded plate covering and shielding said conducting plate on the side opposite said casing, whereby currents from said sourceare required to traverse the entire length of said plate before reaching the connection to said circuits, and whereby the sensitive leads within said case are protected against disturbances traversing the connection from said source.

7. In combination with a radio receiver having a grounded metallic container, said radio receiver having a plurality of tubes having circuits to be supplied with current from a source external to said container, a condenser element comprising a conducting plate secured against one wall of said container but insulated therefrom, said plate and a portion of said container forming respectively the two electrodes of a substantially inductanceless condenser, said-plate having at opposite ends a pair of terminals extending in opposite directions, one of said terminals passing through said container and being insulated therefrom whereby one terminal projects outwardly from said case and one projects inwardly in said case, a connection from said outwardly projecting terminal to said source, a connection from the inwardly projecting terminal to the circuits of said tubes, an inductance interposed in the connection within said case from said inwardly projecting terminal to said circuits and a grounded plate covering and shielding said conducting plate on the side opposite said case, whereby currents from said source are required to traverse the entire length of said plate before reaching the connection to said circuits, and whereby the sensitive leads within said case are protected against disturbances traversing the connection from said source.

MARION J. PIFER. 

